title: T₁ estimation for aqueous iron oxide nanoparticle suspensions using a variable flip angle SWIFT sequence.
abstract: OBJECTIVE
  T1 quantification of contrast agents, such as super-paramagnetic iron oxide nanoparticles, is a challenging but important task inherent to many in vivo applications in magnetic resonance imaging. In this work, a sweep imaging with Fourier transformation using variable flip angles (VFAs-SWIFT) method was proposed to measure T1 of aqueous super-paramagnetic iron oxide nanoparticle suspensions.
  
  
  METHODS
  T1 values of various iron concentrations (from 1 to 7 mM) were measured using VFA-SWIFT and three-dimensional spoiled gradient-recalled echo with VFAs (VFA-SPGR) sequences on a 7 T MR scanner. For validation, T1 values were also measured using a spectroscopic inversion-recovery sequence on a 7 T spectrometer.
  
  
  RESULTS
  VFA-SWIFT demonstrated its advantage for quantifying T1 of highly concentrated aqueous super-paramagnetic iron oxide nanoparticle suspensions, but VFA-SPGR failed at the higher end of iron concentrations. Both VFA-SWIFT and VFA-SPGR yielded linear relationships between the relaxation rate and iron concentrations, with relaxivities of 1.006 and 1.051 s(-1) mM(-1) at 7 T, respectively, in excellent agreement with the spectroscopic measurement of 1.019 s(-1) mM(-1) .
  
  
  CONCLUSIONS
  VFA-SWIFT is able to achieve accurate T1 quantification of aqueous super-paramagnetic iron oxide nanoparticle suspensions up to 7 mM.
authors.affiliation: Bioimaging Research Center, University of Georgia, Athens, Georgia, USA.
authors.forename: Luning
authors.initials: L
authors.lastname: Wang
authors.forename: Curtis A
authors.initials: CA
authors.lastname: Corum
authors.forename: Djaudat
authors.initials: D
authors.lastname: Idiyatullin
authors.forename: Michael
authors.initials: M
authors.lastname: Garwood
authors.forename: Qun
authors.initials: Q
authors.lastname: Zhao
mesh_terms: D000465:Algorithms; D003911:Dextrans / Q000032:analysis* / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000032:analysis* / Q000737:chemistry*; D012815:Signal Processing, Computer-Assisted; D013535:Suspensions; D014867:Water / Q000737:chemistry*
chemical_list: D003911:Dextrans; D058185:Magnetite Nanoparticles; D013535:Suspensions; C097921:ferumoxtran-10; D014867:Water
keywords: T1 mapping; positive contrast; super-paramagnetic iron oxide nanoparticles; sweep imaging with Fourier transformation